Various types of adhesive films comprising a flexible substrate and an adhesive layer have been heretofore available. Such films are provided in the form of sheets, tapes, strips, labels, tags, and the like. Those films having a pressure sensitive adhesive layer generally are mounted on some type of release liner or other releasable support to protect the pressure sensitive adhesive until the film is ready to be applied to an intended article. The film is then stripped from the release liner and applied.
Typically, the substrate for such a film is a self-supporting web or a sheet of paper, cardboard, plastic, or metal. One major face of the substrate has a pressure sensitive adhesive while the other major face can be further coated and/or printed on. Such coating and/or printing can be accomplished either before or after the application of adhesive to the first major face. Other versions of adhesive film have adhesive coating on both faces of the substrate and are known as “double sided” or “two-sided.”. Adhesive films of this basic construction are manufactured for a variety of commercial and consumer uses including labels, tags, and stickers for industrial and consumer products, decorative films for furniture finish and wall covering, tinting films for building and automotive windows, and antiglare films for computer displays. Such films constructed in accordance with prior art are substantially impervious to air and liquids. This condition is due to a variety of practical considerations including the choice of materials and manufacturing processes used, and requirements for appearance and function.
Problem: When an adhesive film according to the prior art is applied to an article, air tends to become entrapped between the adhesive and the article surface. This condition is shown in FIG. 1. To prevent such entrapment and the resulting bubble, a considerably high level of skill is necessary during the application step. Consequently, a great amount of labor and time are necessary to perform the bonding application step. Tolerance for errors during the bonding step is very low because the bond strength rises with the passage of time, which makes it more difficult to peel the adhesive sheet from the substrate article and reposition it at later time. When air bubbles are trapped between the adhesive layer and adherent article surface, the appearance of the film is negatively impacted. This condition is highly undesirable especially when the film is used for decorative purposes.
Even when the film is applied to the article surface and trapped air bubbles are avoided, lifting and formation of bubbles can occur at the bond interface when the film is exposed to environment such as heat and light. Exposure to ultraviolet light is considered especially deleterious. This is particularly detrimental to the appearance and functionality of transparent films such as employed for tinting of windows used in buildings and automobiles, and antiglare films used for electronic and computer displays (flat panel, cathode ray tube).